We are developing sensitive mass spectrometric tools for defining oligosaccharide structures _ especially for those derived from glycoproteins. The task is challenging because of the intrinsic complexity of oligosaccharide structures and because the mass spectrometric response for underivitized carbohydrates is frequently low. We are investigating a new method for derivatization of oligosaccharides. In this method, an oligosaccharide is efficiently ligated to a highly basic aminooxypeptide by the oxime formation reaction. This derivitization method has increased the MALDI-MS sensitivity by up to three orders of magnitude and has allowed us to successfully impliment a powerful glycosidase array carbohydrate structural analysis stategy (Zhao, Kent & Chait, Proc. Natl. Acad Sci. 94, 1629-1633, 1997).